upgrading stuff possible?

just wondering, i live in brasil and its hard to get upgrading stuff once we have nothing to do with the older parts most of the time. stores want only to sell the new products and wont get our stuff as a part of the payment. what do you ppl living in USA and other locations use to do with the older parts when upgrading them?
if you get giving yours as a part of the new parts payment, how much do the stores use to evaluate the older parts? is it a worth deal?

I live in California, and no store will take old computer parts. It seats on the desk or closet and collects dust. Me and my friend gather old parts until we got enough left over to build another, abiet slow, computer. Them we give it someone who doesnt have one. At least they could use it to surf the net or word process on it

There's no system for upgrading. We have to sell our junk to somebody who wants it.

I finally gave up on selling my stuff and did what gtsimmo and his friend do, except we discovered that our old parts are worth buying when turned into a whole computer.

$250 buys our:
750Mhz Athlon (1Ghz Athlon on 100Mhz mobo)
32mb sdram video card (3DLabs)
56k modem
6Gb hard drive (5400rpm)
Windows Me (Compaq CD-ROM restore set)
Compaq deluxe tower (with nifty "window" bay cover and "Frankenputer" decal)
Compaq 100Mhz mobo (133Mhz channel dead)
Norton Utilities Version 3 (CD-ROM)
wheel-mouse (no keyboard)

NO ram
NO sound card

(not for sale by mail)

you could alwyas use old parts to build a server for a lan-party